The present invention relates to a device for tightening a chain used in a chain saw. Preferably, the invention relates to automatic tightening of a chain of a chain saw used in a multi-purpose head of a harvester.
FI 945 240, FI 100 779, WO 98/34 768 and SU 745 440, for example, disclose related inventions.
The prior art, however, suffers from considerable disadvantages. It has thus been problematic to provide a sufficiently simple, reliable and durable structure of the tightening device. The existing solutions also suffer from great difficulties in solving, in a sufficiently reliable manner, both the tightness of oil and fluid channels in the chain saw and the sufficiently small tolerances between the parts of the device ensuring accurate and reliable operation of the chain saw.
In the known solutions, the tightening device attaching the saw flange to the chain saw is supported by the bearing piece only on one side of the axle of the motor controlling the saw. Hence, the guides enabling the tightening movement of the saw flange have to be short in order for the parts of the tightening device not to overlap the saw flange too much so as not to extremely disadvantageously shorten the effective length of the saw flange of the chain saw, and, thus, the effective sawing diameter.
An object of the invention is thus to provide a novel solution so as to enable the above-mentioned problems to be alleviated. Such a device of the invention is reliable and durable, efficiently preventing environmentally harmful substances from being discharged to the environment from the tightening device. The solution of the invention also provides the chain saw with as long an effective sawing diameter as possible.
In a preferred embodiment of the invention, an elongated opening or a slit, in which the axle of the motor controlling the chain can be arranged, is arranged in the tightening device receiving the flange of the saw, thus enabling, however, the mounting piece to move with respect to the axle of the motor. In this manner, the supporting points between the tightening device and the bearing piece connecting the device to the frame of the multi-purpose head can be arranged parallel with the longitudinal axis of the flange on both sides of the axle of the motor.
Considerable advantages are achieved by the invention. The supporting points of the tightening device of the saw flange can thus be dimensioned lighter while they simultaneously allow relatively greater manufacturing tolerances or wear before the operation of the chain saw deteriorates. Hence, the device of the invention can be made more resistant to wear and great forces than the known solutions.
When the device of the invention is used, necessary maintenance intervals can be longer, so the device significantly affects the working efficiency of forestry machinery by reducing inoperative time due to maintenance.